1) The 1990 elections were for a 7 member collective presidency. Results were as follows: Izetbegovic and Abdic from the SDA, Plavsic and Koljevic from the SDS, Kljuljic and Boras from the HDZ, and Ganic, also from the SDA, who ran and was elected as an "Other" candidate.
2) There was nothing in the Bosnian constitution awarding the head of the collective presidency to the winner of the most votes.
When all was said and done, the head of the collective presidency (SDA), the office of prime minister (HDZ), and the presidency of the national assembly (SDS) were divided amongst the three largest parties, making Izetbegovic's position a function of partisan politics, not an anti-Abdic conspiracy.
And your source is? Because I couldn't find a single source supporting your assertions. All of those I searched support Abdic as the clear winner and should have assumed the presidency, but didn't.