You’re appropriate, it’s a poor sign due to the cable or adaptors.
There’s a variety of misconceptions about HDMI that you simply both get the sign otherwise you don’t and this an ideal instance of what occurs when the cable is flawed or a weak sign (as a result of the cable is just too lengthy or a number of adaptors).
HDMI has error correction constructed into the usual and there’s simply an excessive amount of to deal with in order that’s why there’s the odd pixel right here and there which are incorrect.