There is generally a complete misunderstanding of what this means.
Guruji did not mean yoga is 99% physical activity and 1% philosophy!
He meant that the theory of asana is quite simple - vinyasa, drishti, breathing, bandhas - this is the 1%. The theory of Ashtanga Yoga is quite simple: its a method of purification going though sequential steps. These are the theoretical explanations for the simple practice of Tapas. But sadhana (practice) also includes Svadhyaya (self study and study of scriptures) and Ishvara Pranidhana.
What Guruji meant was that there is no benefit from, or possible understanding of yoga without practice. One cannot understand the theory without practice because one cannot understand the context in which yoga is to be understood. Practicing asanas expands the mind in ways which cannot be categorized - only with a glimpse of where yoga is directing us through practice does understanding of the goal become apparent. As Guruji often said - you cannot explain the taste of honey - you have to taste it to know it.
The practical part of the internal yoga is bringing the mind to the point of realization. The theory part is: yogaschitta vritti nirodhah - if you can control the mind then you can experience the Self - this is the theory part.
According to Shankaracharya, Self Realization can not happen through any action (yoga), but only through knowledge (sankhya). The way to know the Self is through study, internal questioning and meditation - these are all internal practices.
Reading Patanjali Yoga is practice, reading the Gita is practice. Mastery over the philosophy is much harder than mastery of the asanas for most people - which is of course why the asanas come first - "Asanas are kindergarten" - as Brad Ramsey says in the Guruji book.
Patanjali defines practice as "the effort to establish steadiness of the mind" - the effort to achieve chitta vritti nirodha. This requires 999% practice!
The practice of yoga in India had been in decline for many years, and so Krishanamchrya and Guruji, funded by the Maharaja, were like missionaries going out into the community and trying to inspire people to take up the practice.
As pioneers in the revival they encountered resistance and negative comments since yoga had fallen into disrepute, being viewed as something only for holy men who renounced worldly life. So Guruji's intention was also to counter the opinions of academics or pundits who professed to write about yoga without having the slightest practical experience with the art.