My partner (28M) whispered "I hate you" when he thought I (37M) was asleep. Do you think he means it?

Me (37M) and my partner (28M) have been together for seven years. We've had arguments in the past and almost broke up more than once. The arguments have calmed down and gotten less frequent over the years. We had an argument today while making dinner. I put the dry pasta in the pot before putting in the boiling water from the kettle and this really got him angry. I was supposed to heat up the water in the pot and then put the pasta in. He stopped talking to me the rest of the evening. He went into a different room and I went to bed. At about 2am, he came into the room and he thought I was sleeping and whispered "I hate you" and walked back out. I tried to go talk to him at around 2:30am but he is not responding to me, just sitting on his iPad. He may be calmed down by tomorrow. What are your thoughts on this?