Yes, this was IBM's symbol for a FET. They had their own nonstandard symbol for bipolar transistors too, three stacked boxes labeled N, P, N, with a triangle on the emitter. (See page 1-4 of the document above.) IBM also had their own logic gate symbols: an OR gate looked like an AND gate, and an AND gate looked like an op amp.
I came across the FET joke while looking up IBM transistor symbols in response to TubeTime's thread on the history of transistor symbols (which is an interesting thread you should read): https://twitter.com/TubeTimeUS/status/1249023089528078337
IBM used all sorts of non-standard terminology of their own. You'd hear their folks seriously talking about PELs instead of Pixels ("Picture Elements"); and DASDs (pronounced "dah-z-dee") instead of disks ("Direct Access Storage Device"). Not clear if it was intentionally designed to be alienating to outsiders, but it sure seemed cultish.
I think several factors led to IBM's non-standard symbols. The standards didn't exist at the beginning, so different companies used different things. IBM also had historical baggage, wanting to stay consistent over time. In some ways IBM's symbols were better, for instance making NPN vs PNP obvious. Finally, IBM was big enough that they could do their own thing and train their own people.
I came across the FET joke while looking up IBM transistor symbols in response to TubeTime's thread on the history of transistor symbols (which is an interesting thread you should read): https://twitter.com/TubeTimeUS/status/1249023089528078337