You’ll probably find what happened is some other website listed the product £4 cheaper.
Big places like EBuyer, CRC, etc, have pieces of software that will automatically scan the internet and match the lowest prices of competitors as long as they are above cost.
Then there are also “Mail Order” shops that some people run from their home, without a shop front – what these people tend to do is work a normal job and then come home and pack orders in the evening. Because they can’t chase the best prices all day they run off of feeds, and just whack a percentage on the top of the feed (without holding the stock.)
When a supplier has a good price, and someone with a feed gets hold of it, sticks 2% on the cost, ruins the market for everyone, and then you end up with the biggies like CRC automatically matching the low cost.
At least this happens in the IT industry all the time. Wouldn’t be surprised if it worked the same as bikes.