That is just an estimate. Most games of this type that are overly big have png images. And by switching from png to jpg or better lossy webp a size change can easily happen from 2MB to less than 200KB per file. You just fiddle around with the compression setting till you would notice the quality loss. Factor 10 is a good starting point for testing out the quality loss. You might see some slight dithering at sharp edges like the black dress and skin, but you should not see any changes in the face till you go down in size further.

There are other tricks, that depend on your creation process. Like separating backgrounds and characters. Lossless compression as in png is for buttons that should be pixel accurate. 

Anyway, if you are at the beginning and would have continued in that fashion your game would quickly be several GB big.

Edit.

Uhm. I have no idea what you did compress or how, since I did not download the big version. But your images are png. You can make that images folder from 74 MB to less than 10 MB without effort or quality loss. And if you do things like make the bra a separate image and overlay it with the engine, instead of in the pic, you can do even more, but that would be overdoing it at the moment. But it is a hint how games only 2GB big can have a huge amount of different images.

They probably also do not have the amount of videos you have. I have little experience in video compression for such games. But if you add more images, consider switching to lossy webp.

Edit 2. Fun short game. But it is rock papier scissors and that exhausts it's fun factor quite quickly as a game. Animations look good in combination with music and voice.

And as clarification, my comments above were for the pictures. How to compress videos like your's, I have little knowledge.