How are words/phrases added to the library and suggested text when they haven't been used together?

[AC Question]

how are words/phrases added to libray and suggested text when they havent been used together.

My phone suddenly has a bunch of suggestive/ sexual words. I didn't add them or type them ever in my phone. Is it possible these were added on their own or that my phone has a virus? It's embarrassing that if I type "hot" the predictive text brings up "girls" & "sexy".

phone was htc0ne m9