I don't think anyone would say it was a "coup"
per se, but they might say that it was an "attempted coup". To determine whether that expression is correct, we have to consider what the intended outcome was, and how things would have likely played out if the mob had encountered even less resistance.
Obviously it seems that one of their targets was the VP, and I can't imagine they would have let Nancy Pelosi continue as second in line to the presidency. There was also the strong possibility of enough fatalities occurring that the Democrats would lose their majorities in both chambers. Perhaps most importantly, the boxes containing the electoral votes could have been captured and the votes destroyed, putting the constitutional process in uncharted waters.
So imagine the situation, where the joint session cannot continue, and Trump sends in his hand-picked troops to "secure" the Capitol. Congress has to amend the Electoral Count Act to clarify how the votes should be counted if the certificates have been physically destroyed. In conditions similar to those at the passing of the Enabling Act of 1933[0], we could imagine Congress deciding to fall back on the procedure outlined in the 12th Amendment for "if no person have such majority". Arguably that would be the correct procedure even without a change to the ECA.
The outcome would thus be for Trump to win the vote by 26 states to 24, maintaining his presidency through means outside the legal and constitutional order. That would naturally and correctly be called a self-coup or autogolpe, in my view.
[0] https://en.wikipedia.org/wiki/Enabling_Act_of_1933#Preparati...