You're both right, and that's the problem.

And it only gets more complicated from there.

In storage 1GB is 1000MB and 1MB is 1000KB and 1KB is 1000 bytes..... This is almost exclusive to hard drives. The rest of the industry uses what is now known as KiB, MiB and GiB, or kebibytes, mebibytes, and gibibytes. 1GiB is 1024MiB, and 1MiB is 1024KiB, and 1KiB is 1024 bytes.

If you're not talking about disk storage, then 1MB is 1MiB (1MB can be either 1024KB or 1000KB depending on context). The terms GiB/MiB/KiB were created because of the confusion between 1024 and 1000 for each jump in size, it's a relatively new term created to increase clarity between the various definitions, where MiB will always be the 1024 KiB version, and MB can be either; in this way, HDD manufacturers don't need to change anything that they are doing, and the industry can have a pure term, free of the confusion created by the disk drive industry.

To bake your brain even more, datacom uses 1000 instead of 1024 for increments, so 1Kbps is 1000bits/s and 1Mbps is 1000Kbits/s. So data transfer, link speeds and throughputs are generally going by the 10base numbering instead of the powers of 2.

The whole thing is a mess, and everyone wants to be the "will acktually" person to correct people about MB vs MiB and none of it actually matters, it's an entirely stupid situation created because the data storage jerks wanted to be able to put a slightly bigger number on their box to say how much capacity their drives had by just omitting the extra 24 bytes per KB, and extra 24 KB per MB, etc. So their product would look like it's bigger than it is.

Arguing about it is pointless.