The implication is probably three-fold when buyers with agents call listing agents. First, they may possess little patience. We live in a world where everybody expects immediate responses from everybody, which is insane. Second, they might not feel their agent knows the best questions to ask or is too inexperienced or not attuned to their needs. Which means in their mind, they feel they can do a superior job. Their agent is just in the picture to write the offer. Sounds insulting to buyer's agents if you ask me.
And third, they might not really understand how real estate works today. They could be old school, like back in the day when almost all agents operated as dual agents. You can read more in my personal blog today at this link: Buyers With Agents Calling Listing Agents, Why?