25-28mm body length is quite a considerable size. I think a cousin of these is often dubbed the "UK's largest spider", even though it technically isn't. But they are up there. Yes, the US has tarantulas, giant house spiders and some larger wolf spiders, but Dolomedes is up there as well.
Even if that particular picture was AI (I don't think it is), there is nothing surprising or exaggerated going on here. More like it's a rather rare/undocumented behaviour. Bit it's totally within the capabilities of a fishing spider.
Yep, they are generally opportunistic and can be quite brazen. But most of the time they'll go after easier, smaller prey.
I used to have a goliath birdeater and it was entirely fed on crickets. We tried a baby mouse once, but it was a huge mess to clean up and they don't need nor prefer it.
I don't think it's a change in their eating habits, these spiders are known to catch fish, frog, salamanders or basically anything that size you'll find near water. Just rare to see and snap a picture of one with a turtle.
We literally have to be very careful of how we definie "life" so we don't accidently include too much stuff we don't want to be life. That's why viruses are usually not considered to be life, even though some people think they should be included.