That came despite Glasgow heading into the break trailing 19-12, and they fell ten points down early in the second half.
That's when Seymour, a first-half try-scorer, completed his hat-trick with two scores in as many minutes.
His fourth late on was the cherry on the cake and Townsend admitted that defensively Glasgow hadn't been good enough in the first half.
"It was a great reaction in the second half," he said.
"We came up against a very good team. They were able to produce really quick ball in the first half with line breaks, and we should have been further behind at half-time.
"We weren't on our game defensively in the first half. I am delighted that we got through… thanks to Tommy, who played a massive role. He's in fantastic form. Last week he was outstanding and he is finishing really well."
Seymour looks to be in the form of his life, with six tries in two games so far this season, and the winger believes there is more to come.
"It was pretty special," said Seymour.
"I hope I haven't run the well dry yet. I'm incredibly happy and thankful for the guys inside me having that ability to put those passes in and put me away.
"It's a huge win going forward.
"It's very early on in the season - we're obviously incredibly happy, and it's a huge momentum boost beating two quality opposition like that, but we're not getting ahead of ourselves.
"We had the harsh words at half-time and talked about the things we needed to correct, but that's the positive thing about us, we're harsh on ourselves, we're sensible when it comes to taking on the advice that we're giving each other.
"We're not panicking, we're not trying to force things - if you start trying to chase things that aren't coming naturally you often find yourselves on the end of the bigger margin."
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