VFR non-ADSB tracks in Flight Aware frequently have spurious positions inserted in them.
I cruised home from Cincinnati one day at 17,000 in my Navion. Some of the highest ground speeds I'd ever seen (260 knots).
To be fair, I was using orographic lift for a lot of it (the wind hitting a ridge and rising, with you in it).
Although yes, I was attempting to maintain some semblance of Vy adjusted for altitude. Especially near the end, there was a pretty fine line between climbing feebly and descending, really just a few knots (or mph in my case).