I think the bowl was "grouted" to the floor. Every once in a while you will see someone suggesting "grouting" a bowl to the floor. This is how you remove them.
By the way, the homeowner assured me it was a perfectly fine toilet bowl, but that the drain line wasn't working well. I told him it was likely in the trapway; which we may never have known, but since the bowl was "stuck" to his floor, and the only option was to break it off the floor, this is what I found. You have to be very careful with broken porcelain. Years ago I was going to do the STP, Seattle to Portland bicycle ride of 200 miles in two days. Friday morning before the weekend, I reached around a broken tank to get to the bolt, and sliced the side of my wrist and brushed the tendon. The slice in my arm was about 3" long and was dripping out red fluid all over the floor, which was puzzling because I didn't know where it was coming from. When I looked down at my arm I realized it was "my" red fluid.
That killed the 200 mile bike ride for me.