Just sharing my experience from last March 2018
I had one piece of watermelon,1 banana, and an apple in my purse to eat for breakfast--early morning flight. I told them and I was not fine.
I was escorted by US customs into a briefing/holding area and told no fruit can go into the USA from Canada (even if I was going to eat it at the airport on Canadian soil).. This man (Customs agent) was rude,discourteous and downright ignorant to me.
The pregnant mom beside me who had packed baggies of clean fresh veggies(Vegan) was also spoken to in the same manner.
This agent told me to NOT go by what is posted on TSA https://www.catsa-acsta.gc.ca/en web page as it has nothing to do with US Customs.
So in my opinion I would not take any fruit or veggies into the USA.
Hugs Mel
Sorry you had such a crappy experience. I don't know if that's normal now, or if you just got unlucky. We once tried to bring a Florida orange into the US pre-clearance area at Ottawa airport. We'd decided to go to the airport early in hope of getting out ahead of a nasty winter storm, and anticipated a lengthy wait. It was completely our intention to eat the orange long before leaving Ottawa, and this was not that many years after US pre-clearance was opened in Ottawa, so I guess we weren't really thinking of it as "entering the US" before we'd even left the airport. Anyway, we declared it, the agent took it, and that was the end of it. No lectures and no escort to a separate area, just "sorry, I have to take this" (or something to that effect).
We've also taken small amounts of prepared fruit (washed and generally pre-cut) in at ground crossings on multiple occasions. We always declare it, and usually just show them what we have, since it's typically close at hand, not packed away. We've never had a problem, but then we now know better than to try to take in citrus fruit!
This thread also reminds me of a time when we were coming back to Canada (so this was Canadian customs, not US), and the agent asked if we had any fruit or vegetables. I started to say no, and then changed it to "wait, yes, I have half a Subway sandwich that I didn't finish eating", and the agent literally laughed at me and sent us on our way.
Unfortunately there doesn't seem to be one single answer for "what's okay" or even what kind of response you'll get if declaring something that's not allowed. Personally, I wouldn't try to take something that I know is going to cause a problem (whole citrus in particular), but otherwise I'm comfortable declaring what I have and letting the customs officer tell me if it's okay on that day or not.