There was significantly more than just "your word is your bond". Additionally, it's not the fact that some of these thoughts were in both. It was a combination of multiple phrases occurring in both, word for word, and that these particular phrases all were grouped together with a similar contextual flow and format as the both.
Had Melania talked about how she had values impressed upon her to work hard for what you want in life, and then talked about how she did that. And later on in talking about her husband and why he should lead, she spoke about how "your word is your bond", and then near the end started talking about wanting children to know their only limit is their dreams.....it still would had perhaps looked questionable, but it wouldn't be as clear cut of a case as this.
But you can literally take a couple of paragraphs, without editing, and put them directly side by side to see multiple words, phrases, and sentences that are near or exact matches. Having full paragraph sized thoughts and ideas coming out in exactly the same fashion as someone else is extremely less likely than a notion of two people who happen to, for instance, utter a common phrase like "your word is your bond" at two randomly different sections of a speech.