Sanpatel,
It may be an infection of Fusarium fungus which causes Mango Malformation disease; if you cut it off, you did the right thing. I hope you sanitized your clippers or saw, before doing any other cuts.
Mango Malformation typically makes a much tighter ball of buds, with no leaves developing; that is why I am not sure that your tree has it.
I saw one similar case, with less-narrow leaves, at a commercial mango grove in western Florida. My fertilizer had never been there.
If Boron is at issue, it is deficiency, not excess. Excess causes blackish brown marginal burns on leaves. Deficiency causes tip die-back and buds that don't develop properly. So this actually could be the problem. The fertilizer manufacturer did change my customer-request-formulation, reducing all the micro-nutrients, including Boron.
Another possibility is volatilization of an herbicide being applied up-wind, even on another property, or weed-and-feed application anywhere within five times the radius of the mango's canopy.