The 21-year-old hitman, who joined Rovers on a half-season loan from Newcastle in January, scored twice at Fratton Park - including a last-minute winner - to make it three goals in two games for the League One side.
Mowbray knows all about the youngster's prowess up front after Armstrong previously recorded a 20-goal season under the 54-year-old at Coventry.
"I’ve managed Armstrong before at Coventry, where he scored 20 goals," he told The Lancashire Telegraph.
“At his best, he’s electric. He lives for scoring goals. He’s fast, shoots off both feet, can play No 9, off either side or at No 10, and of course we’re delighted he’s scored the goals.
“I thought it was right for him to start. I thought Armstrong’s qualities would have given them problems and that was the case.”
There has been a bit of buzz around the Newcastle product for a while, following on from his red-hot form for the Sky Blues on loan.
But the fact that he only scored once in 20 Championship games for Bolton during the first half of the campaign should be a big reminder as to why fans of the St James's Park club shouldn't get carried away.
At this moment in time, he seems a million miles from being ready to score regular goals in the Premier League, though he is young and another goal-laden stint in League One will do his confidence the world of good.