Files with long numeric strings are frequently used to share memes, but they are also a common format for malware or phishing links.
A very small file (under 1MB) is likely a short meme or a GIF-style loop. 5125212941360038568.mp4
This specific numeric format is how Discord renames files uploaded to its servers. If you found this in your computer's cache or a shared folder, it likely originated from a Discord chat. Files with long numeric strings are frequently used