It is not racism. Scots = Irish genetically.
This is called sectarianism and comes from Northern Ireland.
The individuals concerned were doubtless from the Glasgow area where sectarianism is rife among the lower orders of society who are of Northern Irish ancestry.
This behaviour is most unusual in Edinburgh and does not exist in the universities. They will pull your leg about being Irish though! But only in fun.
P:S: Mr Og's comment criticising the Unionists is unworthy of him. The Scottish Unionist Party has little to do with the bigoted nutters in Northern Ireland. For details on what is now a fringe of the Scottish Tories See
http://www.scottishunionistparty.co.uk/.