Yeasts are fungi???

In short, yes.
Fungi include single-cell groups like yeast, and multicellular groups like mushrooms, 雪耳, bread mould, slime mould, etc.
Fungi (singular fungus) are a kingdom of eukaryotic organisms. The fungi are heterotrophic organisms characterized by a chitinous cell wall, and in the majority of species, filamentous growth as multicellular hyphae forming a mycelium; some fungal species also grow as single cells. Sexual and asexual reproduction is via spores, often produced on specialized structures or in fruiting bodies. Yeasts, molds, and mushrooms are examples of fungi. The discipline of biology devoted to the study of fungi is known as mycology.