I just took a look at the account in question ontop.lifestyle and its clear to say he has purchased around 5k followers, and has purchased a ton of likes on his picture.
1. Look at his likes, and see how many of the likes came from his followers, and how many likes came from accounts with little to no followers, but are following a ton of accounts. Also look at the accounts profiles, and see what pictures they have liked. If it looks completely random, they are like bots. Also notice the irregular vast difference in likes on each picture. Some have 800 likes, while some 12k. That does not happen on an account with real, active, and targeted followers.
2. Look at his followers, use the same method as above, and its clear that he has purchased bot followers.
3. In regards to the remaining real followers, he has gained these by getting his pictures in the Top Post section from buying 1-10k likes on the pictures. This results in hundreds of new followers every day, and a ton more likes since his pictures are being featured and showcased to millions.
If your looking to buy this account, your are looking at a horrible investment.
Also note for buying IG accounts, never buy accounts with over 10k followers. Over 70% of them are full of fake likes and followers. The remaining 20% are scammers who use a easy little trick to sell, recover, and re-sell the accounts. I have seen a few accounts with 1m+ followers being sold, and less than a few weeks later they are back on the market from the same seller under a different username.
PS: I buy and sell IG accounts on the side, and have a very extensive background check before purchasing accounts.