Slightly, if your child does something well and you claim credit for it when there is real debate about how much influence you had over it, then yep, that's smug.
Statements like 'I don't think it has that much to do with luck after the 4/5 month point. You are lucky if you have a newborn or very young baby that sleeps through, after that point I think it's down to a lot of other things, but not really luck.' in the context of your own children who have cracked sleep relatively early does come across as smug.
I tried very hard not to be smug when I had a 10 week old who went down to sleep at 7pm every night, having set his own bedtime, had a dream feed at 11pm and then slept until 6am because that was nothing to do with me, really.
Just like when it all went horribly wrong between 7 months and 18 months, it wasn't my fault and others weren't superior parents because, having tried the same strategies and put the same amount of effort in, their children had responded and mine hadn't.
For the record, he's a brilliant sleeper now at 2.5. But we had to put a lot of effort it and, crucially, recognise at some points that he was not ready, even though other people's children might have been.