Thank you, ahvalj, it all makes sense now.In the 18th and early 19th centuries, this shape was also used in print, compare this grammar printed in 1755. In pre-typographic times, this was also in use as a variant. I guess it represents an evolution from the regular T via this and this shape (note in the latter case how the height of lateral outgrowths varies in individual instances of T).
I think you are right.Looks like an individual ornate way of writing (i. e. the italic т I mentioned but with embellishments).
It is, however, commonly used in printed italicized texts, even in textbooks for beginner learners of Russian. There are at least two such books available in Hungary and neither of them explains why торт becomes mорm.By the way, while the variant you mention is taught in school, many (most?) kids eventually change it some time at middle school into a plain italic т.
That's what my Russian teacher said.In byzantine calligraphy, often the capital T has some decoration hanging from the 2 ends of the orizontal bar, like this https://kentroglossatexni.files.wordpress.com/2014/11/13.jpg
This decoration if elongated, can make a T looking like M.