Yes, but why the letter "כ" chaf is here? In the notes, there is no that form. Moreover, the first person singular past only justify the use of the suffix "תי", as in the notes. I'll remain to research about this topic.
The כ is one of the three root letters of the verb אכל. The first person past tense for regular verbs in the Pa'al binyan is סססתי (where I have used ססס for the root letters), so in this case it becomes אכלתי. Hope this helps!