No. I work for an OTA (not Kayak). First of all airlines file their fare rules and OTAs don't change the prices, and generally airlines pay around $10 to us to book a RT fare so there is little room to discount. Kayak is a meta which means all they do is present prices they are given from their partners (either via a feed or scrape) and then send them to the partner who shares the fee. Southwest (as others have mentioned) is not available in the US as a business choice. Kayak also heavily caches the fares (everyone does to make performance better) and inventory changes a lot especially in close by dates. Seeing cached prices of a cached price means the actual price can change a lot from searching to booking. Note the final price is
only
determined when you hit a booking page, everything before that is cached and might be fairly stale. Of course they can be errors in pricing since the fare rules are crazy complicated and often the difference in fares might be all the taxing entities. Each country, county, city, airport and cow pasture might affect the final price so it's possible that a country where you are booking might affect this (our customers are mostly in the US) but I doubt it.
tldr - lucky "hacker"