'Histogramed' or 'histogrammed'?
Consonant doubling can occur before the verb inflectional suffix -ed even when the verb does not have a primary stress on the last syllable of its base form. There isn't really any simple rule for when this happens. You can see some attempts at formulating more complicated rules in Alex B.'s and Patricia M's answers to the following question: "Focussed" or "focused"? Rules for doubling the last consonant when adding -ed
The spelling histogrammed is likely based at least in part on analogy with the more frequent word programmed. There was a previous question about the forms of that verb: “Programming” versus “programing”: which is preferred? I use -mm- spellings for these words and also for diagrammed and anagrammed.
The use of double consonant spellings for -gram verbs is probably related to their pronunciation, and possibly to their etymology.
They are pronounced with an unreduced vowel /æ/ in the last syllable. In some theories of English stress, this implies that the last syllable has some kind of stress (even though it doesn't have the primary stress).
The Greek source of -gram, -γραμμα, has a double consonant. The spelling programme is used in British English in most circumstances.
I think the quotation from The Free Dictionary confuses different kinds of examples that would be better dealt with separately. The rules for doubling consonants before the inflectional suffixes -ed and -ing shouldn't be expected to govern the use of doubled consonants in all other kinds of words. In Latinate words, double consonants occur fairly often after unstressed vowels, usually for etymological reasons.
The double -ll- in crystalline and crystallize is probably related to etymology: -ize is a suffix that doesn't only attach to English words, but also to bound Latinate roots (e.g. anglicize). I wrote an answer to a question about the spelling alternation between -our and -or- in words like vapour, vaporise that talks about the general principles for spelling words ending in the suffix -ize (-ise).
Similarly, the spelling of the noun cancellation is based on etymology and for most users of American English, it does not correspond to the spelling of the inflected forms of cancel (canceled and canceling).