i recently sold my macbook and reset the disk drive, but didnt delete anythibg manually. will the new owner have acess to my information if the macintosh disj drive is erased?

This is what you needed to do:

What to do before you sell, give away, or trade in your Mac - Apple Support

It would depend on how effectively you erased the disk. If it was a simple erase of the Directory then all your files are still there, but although they can in theory be recovered they would be in a major jumble and the effort is unlikely to beworth it. Doing that properly is also expensive.

If you formatted the drive then the files should have been erased, possibly in multiple passes - you may have been offered a choice when formattingL the more the better. In this circumstance the FBI might be able to retrive a few files, but not ordinary mortals. On the whole I shouldn't worry about it.

With the disk erased all logins and saved messages will have been erased too. I'm assuming that you formatted the disk and reinstalled the System? Even if you just dragged the Home Folder to the trash and emptied it the same would apply as all the password etc. in there - in theory they could be recovered but the complexity of the task makes it most unlikely anyone would try. Remember that your data is scattered all over the disk in a way that only the computer knows - that's what the Directory is for. Basic apps which attempt to recover data usually produce thousands of files, moslty with no no helpful names, and often incomplete.

When you erase a file by dragging it to the Trash and emptying that is simply deletes the entry from the Directory: the file still exist but as the computer has no record of it it can be over-written. If you dragged your Home Folder to the Trash the same wouod apply.

To erase a disk completely you use Disk Utility to erase and format it - formatting lays out the sectors which the system will use to allocate your data. Pre Catalina this also erased the system, leaving a completely empty disk, so you would have to re-install the system. In Catalina the system is on a separate sector which you can't touch so it remains in place.

Since you said you 'erased the disk I assume you did the latter. This process over-writes the previous contents of the disk. For a more secure erase it can over-write it many times. All this can sometimes leave tiny traces of the original data, but pretty well only the FBI could retrieve anything at all: you don't need to worry about that as you are not a terrorist (presumably).