I didn't use the 50 ohm terminator when plugging directly into the 1S1 because I thought that would be too much load, since the 1S1 already provides 50 ohms of load. However, I tried to replicate the setup as best I could by adding in an equivalent number of SMA adapters, including the tee (with an open end where the 50 ohm terminator was). SMA adapters don't seem to change the waveform noticeably. So I don't think the setup itself is causing the ringing, unless the 0.25 inch unshielded line running from the SMA socket to the solder pad of the probe's input is the culprit.
I already wanted a NanoVNA, but now I feel compelled to also own an TinySA. I need more gift-giving holidays in the calendar.
