Hi,
Both of these files don't exist by default in HikaShop.
So they were indeed maliciously inserted.
Does that mean that there is an open vulnerability on your website ? It's highly likely yes. Maybe you updated your extensions/Joomla in the mean time and that vulnerability has been closed already. The best would be to contact a security specialist like aesecure in order to check on it.
Does that mean that there is an open vulnerability on HikaShop 2.6.4 ? Not at all. It could be, but in that case, it would likely have already been reported and fixed, and many other websites would have been infected, especially ours.
So far, we had only one security issue reported and fixed in 7 years (and it was a few years ago). We try really hard to code in a secure way.