They were slower than the RB, Astons and mercs behind so they knew they had to go a different route strategy wise to beat them. Considering stroll who started on hards and went as long as tsunoda in the 1st stint finished well behind him (at one point in the race, stroll was within 5 secs of tsunoda and at the end he was over 10 secs behind), it seems AT and yuki made the right call

Actually, Yuki himself explained it. I think he meant they wanted to do the one-stop strategy unlike others.

“We were listening to what the tyres say and they held on quite well in the first stint. That helped, I think that was a key moment. I think in the end, what we [did] on the strategy itself was okay.

“Even [if] I did the same exact same strategy as the top teams, I don’t know if we’re able to finish P6 anyway. So I think we don’t have regrets.”

(Actually I wrote another comment saying the same, but at the time I didn't know Yuki's quote. In addition, that comment of mine doesn't show up, so I assume there was an error and my comment didn't register in the server.)