I am the poster. When the spray dried up, I noticed many tiny bugs or mites infesting the whole plant. Didn't want it to spread to my other plants so I threw it out. Didn't seem healthy for some weeks or months.

Sounds like Spider Mites. If they've been on your plant indoors for that long they're probably already on your other plants. They like dry conditions which are readily found indoors. People often get rid of them by wiping the plants down with soapy water. You need to do it often to stop numbers from building up. You can also use miticides which get rid of them if you're not opposed to using chemicals. But you need check all your plants ASAP.

Thank you. Unfortunately I already disposed of it because I was afraid they would spread. This palm was a distance away from other plants, so hopefully all is not lost. Thanks again.