Word for "drawing a decisive conclusion about a phenomenon according to specific personal experience"

The word you are looking for is anecdotal.

Anecdotal (adj): (of an account) not necessarily true or reliable, because based on personal accounts rather than facts or research.

Example: Historic accounts of this era give no indication of any negative impact to fish populations and in fact, anecdotal accounts reflect quite the opposite.

[Lexico]

This Wikipedia article calls it Hasty generalization, but if I were A in OP's example I'd say...

You can't generalise from the particular.

I don't understand why OP says his example is "not only generalization", since that's precisely (and only) what it is. Which arguably makes the question itself pointless, but I'm posting this answer because future visitors might find it after searching for words in the question title.