Is the US really as religious as most europeans believe?

Yes, you experienced the true US.
Europeans are humorous about this issue, in a nice way.
What Europeans imagine to be religion is really Americans' barbaric nature, which is just as fearsome and not to be trifled with.

No, the malls and secular view of life is not just in Florida.
Paradoxically, Florida is known as a "Northern state" because it is like a cross-section of the country and is more-or-less representative of what it's like in other parts.

If you are looking for religion...
Northern Florida, Georgia, the South, and Kansas are where you'll find the Bible Belt and a different state of mind.
You obviously you didn't go to Tallahassee - if you want the full story on the religious part of Florida.

If you are looking for food...
Louisiana, reportedly, has more of that sort of thing.
Also, Hawaii is known for its luaus.

Regarding "barbarians" in humanistic literature:

Confucius’ comments about the barbarians convey a deep-felt optimism about the universality of virtues.
For example, Analects 13:19 suggests that all humans — even recalcitrant barbarians—will recognize and respond to virtues such as deference and respect:
“Be deferential at home, handle public affairs respectfully, and do your utmost in your relationships with others.
Even if you were to go and live among the Yi or Di barbarians, you could not do without such an attitude.”
http://faculty.baruch.cuny.edu/hsarkissian/Sarkissian%20-%20Confucius%20and%20the%20Effortless%20Life%20of%20Virtue.pdf

Yes, you only see the religious fat tards in the bible belt.

religion = stupidity

look at all the stupid people in America ready to vote for Trump.

case closed.

America is full of very stupid, religious people.

The U.S. is not a 'Christian' nation, we are a secular nation. Sure there are some (a vocal minority) who are Very religious, but most of us aren't. The amount of food and prices have much to do with location and the people the restaurants service. Some states have more overweight people than others.

Seeing overweight people largely depends on where you look, but malls are pretty much average.
If you go to a 10k race, you will see very few fat people. If you go to a casino (where people are generally older and wealthier), you will see a much higher percentage of the overweight.

Maybe you need to examine your own bigotry. You seem to have held a lot of unfounded, bigoted ideas about the USA, and your comment about "patriotism lacking in the UK" leads me to strongly suspect that you have a lot of bigotry towards other countries as well.

Also, what makes you equate "being religious" with "asking atheists uncomfortable questions"?

Most of it isn't, but the South is. You were lucky AND you also seem to keep an open mind. There are lots of people from Europe who go to places like the theme parks in Florida, see all the horrible fast food (what theme park anywhere in the WORLD doesn't serve junk?) and then come to the smug judgement that "all that Americans eat are burgers are churros and all Americans are all fat".

Jesus tells us to do our good deeds in secret. If you visit a homeless shelter, a food bank, any charity, you will find the real Christians volunteering without fanfare.
I think you saw the real US.

You won't know how religious Americans are until you ask them.

However, from my point of view, there has been a noticeably steep and sudden increase in secularism here.

I think you would see the religiosity on display more in family homes or churches or certain areas like the Bible Belt.