He dropped it and it's not like his name was on it so they could return it. LN has more detail but leaving items lying around unattended is VERY ILLEGAL. Especially if item comes from a monster not found on that dungeon floor. Not sure about tech level of using dirt or rocks to make things, but all materials come from drops. Wood for furniture, all food whether meat, fish, vegetables, etc., jewels, ores and metals. So if anything is left unattended for a while it turns into a rogue version of the base monster (not sure if it's minutes, hours, or what criteria is.) Rogue monsters are more powerful versions of the base monster like difference between common and elite, or difference between a lvl 1 and lvl 3-5. Since no numbers are shown on monster stats can't say exactly how much difference shown when a rogue is compared to the base monster other than it's enough to be easily noticed. So if those adventurers hadn't picked up that carrot and nobody else came by it would've turned into a rogue slime which could have injured or killed an adventurer who didn't realize it was a rogue monster. So as a result all garbage is required to be carefully collected and burned to avoid it turning into rogue monsters and attacking people.