As you thought, data.info (and any file created by TWRP and with said extension) is a binary file. Given it, I've inspected it with the Linux tool hd, which lets me see an hexadecimal dump along with the decoded output.
Dump of the file
00000000 0c 00 62 61 63 6b 75 70 5f 73 69 7a 65 00 0b 00 |..backup_size...|
00000010 31 33 31 34 36 37 34 36 38 38 00 0c 00 62 61 63 |1314674688...bac|
00000020 6b 75 70 5f 74 79 70 65 00 02 00 30 00 0b 00 66 |kup_type...0...f|
00000030 69 6c 65 5f 63 6f 75 6e 74 00 05 00 37 31 30 37 |ile_count...7107|
00000040 00
|.|
00000041
As you may have guessed by looking at the rightmost column, those kind of files contain information such as backup size and type, as well as the file count.
Before you ask, do not delete those files. Should you do so, TWRP won't probably be able to restore your backup. Delete them only if you're brave and have a backup.