Also, if there was ammonia present and the pH was below 7 before the waterchange it would have been ammonium which is much less toxic. If the pH went over 7 after the waterchange the ammonium will change to ammonia. The toxicity of the ammonia gets 10x worse for every pH point above 7 (10x at pH=8, 100x at pH=9, 1000x at pH=10 etc).
Maybe the Neon’s aren't ammonia tolerant and the other tetra's are. Many fish never develop a tolerance to ammonia as their natural environment never has it present. These are usually the first fish to die when an ammonia spike occurs. Tetra's natural environment is acidic therefore no ammonia... Maybe these Neon’s were wild-caught and the other tetra's were captive-bred. Wild-caught fish are usually more sensitive.