FC Porto escaping with a lone goal in their home is impressive, kudos to them but I don't think they can repeat that when they visit Arsenal at Emirate in second leg.
Arsenal is stronger at home
It is this same overconfidence that killed Arsenal in the first leg. They underrated Porto. Underrating teams from other leagues is something premier league teams and fans have been known for. Arsenal really thought Porto would be a very easy match, a walk over and they were wrong.
Arsenal didn't play well, so I can't say they didn't deserve to lose. They had only one shot on target.
This is the same thing Arsenal fans think about the second leg. They feel because they're at home they would win the match. It is still not going to be an easy match for Arsenal. Arsenal still have a chance to qualify for the next round but they have to take their chances and not underrate Porto.
Arsenal needs to change their mindset about this as well because in last season they lost in UEFA Europa Cup match with same mindset while they were playing against another Portuguese side they were taking them lightly, and they give them shocking defeat at home which eliminate them so now again they are overconfidence, so things can go against them because Porto is surely not easy side, and they are also having quality players which can create problems for them in second leg game.
Here, I am agreed with you about this Arsenal were not good in first leg game and Porto take good advantage of this and not allow them to have any goal which is impressive from them and also good reading by their coach about Arsenal strategy hopefully now in this second leg game we will have better Arsenal which will give their best for the win.